Ted Kaczynski (born May 22nd 1942), widely known as the Unabomber, was also considered a suspect in the Zodiac killings due to his interest in ciphers and his penchant for engaging with authorities, media outlets and victims of his crimes in the form of letters and manifestos. He contacted authorities in 1995 demanding that a 50 page article he had drafted called the Industrial Society and its Future be published in a leading newspaper or journal, stating his murderous bombing campaign would cease if this criteria was met. His reign of terror, killing three and injuring a further twenty-three others, ended on April 3rd 1996 when he was arrested in his cabin near Lincoln, Montana, where Kaczynski was living in remote isolation.
He was captured thanks to his brother's wife, Linda Patrik, who after reading excerpts from the 50 page 'Unabomber Manifesto' while on holiday in France, drew parallels to letters she had been shown by David Kaczynski, that had been written by Ted to newspapers twenty years previously, using similar phrases and ideas. David Kaczynski checked the manifesto and instantly recognised the term "cool headed logicians" previously used by his brother. He contacted the FBI and submitted some writings of Theodore Kaczynski for comparison.
His early bomb making was less sophisticated, inflicting injury rather than death. His first device in May 1978 was placed in the parking lot at Chicago's University of Illinois, return addressed to a university professor Buckley Crist. But the professor, obviously realizing he had never sent any package, contacted campus security, and it was eventually opened by police officer Terry Marker. Fortunately for Marker the bomb had design flaws such as the use of wood, which decreased the pressure the device could generate and he ultimately survived the explosion, sustaining injuries to his left hand.
His next attacks focused on airlines, when in 1979 a bomb was discovered on an outbound flight from Chicago to Washington. The passengers and crew were extremely lucky to survive, but for a faulty timer, the device had enough energy to destroy the plane. A task force was set up and in 1980 John Douglas and the FBI Behavioral Science Unit would initially evaluate the suspect's profile as an extremely intelligent individual, with an academic degree in hard sciences. Meanwhile, Theodore Kaczynski was honing his skills, until finally his art of handcrafted bombs eventually turned deadly.
Theodore Kaczynski claimed his first casualty, when John Hauser, a Captain in the Air Force was partially blinded in one eye and lost four fingers when receiving a mailed bomb in 1985. Hugh Scrutton who owned a California computer store, in 1985, became the first fatality of the bombing campaign, followed by Thomas J. Mosser (an advertising executive) in 1994 and Gilbert P. Murray in 1995, who was the president of a lobbyist timber industry group.
Earlier in Ted Kaczynski's bombing campaign, on June 10th 1980, Percy Wood, president of American Airlines opened a package containing a book called 'Ice Brothers' packed with explosives, from which he narrowly cheated death. The device was constructed using wood - the victim's last name was Wood and the return address was from a street named Ravenswood. Was Ted Kaczynski playing a game of words with investigators in his attempted murder of Percy Wood? Inside the chiseled out section of the book Ted Kaczynski had inserted a small piece of metal in which the letters "FC" had been punched into its face. These two alphabetical letters would be used throughout his bombing campaign to identify his work to authorities. "In all, 16 bombs—which injured 23 people and killed 3—were attributed to Kaczynski. While the devices varied widely through the years, all but the first few contained the initials "FC." Inside his bombs, certain parts carried the inscription "FC," which Kaczynski later asserted stood for "Freedom Club". He is now serving four life sentences with no chance of parole.
The Zodiac link is based around his high intelligence, acquiring a PhD in mathematics from the University of Michigan, having excelled in geometry and calculus, and taught courses at the University of California, Berkeley in 1967, where he was an Assistant Professor of Mathematics. Therefore, the concept of radians and map coordinates used in the Zodiac letters would be well within the capability of Theodore Kaczynski.
Theodore Kaczynski lived in Berkeley during the time of the Lake Herman Road murders on December 20th 1968. Then, in June 1969 he resigned his position and moved closer to his brother David. In the summer of 1969 David experienced the troubled side of Theodore Kaczynski when camping in British Columbia, where an application to purchase government land was rejected by the Canadian government. This seemed only to accelerate the already antisocial behavior exhibited by Theodore Kaczynski. In 1971, he finally purchased some land on the outskirts of Lincoln, Montana, building himself a remote one room cabin, where he would ultimately spend the remainder of his freedom living as a recluse.
His interest in coding and knowledge of bomb making equipment are two of the main reasons people look into Theodore Kaczynski as a possible Zodiac suspect.
However, he has never been linked through DNA, fingerprinting or handwriting analysis, plus he was living in Lombard, Illinois during key Zodiac timelines. In addition, he or his copious quantities of literature have never referred to any of the known Zodiac crimes, despite the fact he has little to lose after receiving his heavy prison sentence, from which he undoubtedly will never see the light of day again. He has since been cleared as a suspect by most people, including the FBI and San Francisco Police Department.
1963 June 4th-The Domingos/Edwards Murders
1966 October 30th-The Cheri Jo Bates Murder
1966 November 29th -The Confession Letter
1966 December- The Riverside Desktop Poem
1967 April 30th- Bates Had to Die Letter
1968 December 20th-The Lake Herman Murders
1969 July 4th-The Blue Rock Springs Attack
1969 July 31st- Vallejo Times-Herald Letter and
408 Cipher Page1 (solved)
1969 July 31st- Examiner Letter and
408 Cipher Page 2 (solved)
1969 July 31st - Chronicle Letter and
408 Cipher Page 3 (87% solved)
1969 July 31st-The Complete 408 Cipher
1969 August 4th- Debut of Zodiac Letter
1969 August 10th- Concerned Citizen Card
1969 September 27th- The Lake Berryessa Attack
1969 October 7th- The Good Citizen Letter
1969 October 11th-The Presidio Heights Murder
1969 October 13th-The Paul Stine Letters
1969 October 22nd-Call to Chat Show
1969 November 8th-The Dripping Pen Card and
340 Cipher (partially solved)
1969 November 9th-The Bus Bomb Letter
1969 November 19th- The Riddler Notes
1969 November 21st-The San Jose Code Letter
1969 November 28th-The Betsy Aardsma Murder
1969 December 7th-The Fairfield Letter
1969 December 10th- Forecast for Cancer
1969 December 11th- Forecast for Leo
1969 December 16th-The Fairfield Letter
1969 December 20th-The Melvin Belli Letter
1970 Feb 21st- The Hood and Garcia Murders
1970 March 22nd-The Modesto Attack
1970 April 15th-The Robert Salem Murder
1970 April 20th-"My Name is" Letter,
Cipher 3 (solved in 2019) and Bus Bomb Diagram
1970 April 28th-The Dragon Card
1970 June 26th-The Button Letter
Cipher 4 (solved in 2019) and Map
1970 July 4th-The Sleeping Bag Murders
1970 July 24th-The Kathleen Johns Letter
1970 July 26th-The Little List Letter
1970 Sept 6th-The Donna Lass Disappearance
1970 October 5th-13 Hole Postcard
1970 October 17th- "You Are Next" Postcard
1970 October 27th-The Halloween Card
1971 March 13th-The Los Angeles Letter
1971 March 22nd-The Pines Card
1971 Unknown- The 148 Character Cipher
1971 July 13th-The Monticello Card
1973 August 1st- The Albany Letter
1974 January 29th-The Exorcist Letter
1974 February 3rd-The SLA Letter
1974 May 8th-The Citizen Card
1974 July 8th-The Red Phantom Letter
1974 December 27th- Christmas Card
1975 November 3rd- The Belmont Letter
1978 April 24th-The 1978 Letter
1978 May 2nd- The Channel Nine Letter
1978 July 19th- The Scotch Tape Letter
1981 March 8th- The Peachtree Letter
1986 May 6th- The Freeway Letter
1987 October 28th- The 1987 Letter
1988 February 1st- The McDonald's Letter
1988 February 8th- The McDonald's Letter 
1990 September 25th- The Celebrity Cypher
1990 December-American Greetings Card
2001 January 10th- Happy New Year Card
Unknown DMV Letter (possibly November 1971)
Zodiac researcher, Dr. Mark Hewitt, goes into extensive detail in his third book Exposed:The Zodiac Revealed, naming Theodore Kaczynski as the Zodiac Killer. Here is a 90 minute podcast interview with Dr. Mark Hewitt, outlining some of his reasons for suspecting the Unabomber as the Zodiac Killer.