Presidential pardon

Presidential pardon exempts a person from any legal penalties or liabilities that would normally result from criminal acts. Transactional immunity refers to the inability of the prosecutor to prosecute a witness in exchange for the witness's testimony, an action referred to as "turning state's evidence." Under use immunity, the government may not use a witness's grand jury testimony to prosecute that person. However, if the state acquires evidence for a crime independent of the testimony, then the witness can be prosecuted.

Pardons on 24
In the world of 24, immunity is often traded to terrorists or collaborators in exchange for information or help in capturing others.

Nina Myers
Immunity (and a full pardon) was given to Nina Myers during Day 2 when she agreed to help Jack Bauer find a nuclear bomb.

Later in the day, Myers had Bauer at gunpoint and demanded a pardon for his murder. Bauer urged President David Palmer to agree to the pardon but he soon realized that until the pardon came through, she could not kill him without being taken down herself. With this information he walked away from Myers, who could do nothing about it.

When she had finished helping CTU, Myers was released.

Patrick Kelly
On Day 3, Sherry Palmer contacted Kevin Kelly and asked him to come forward with information about Alan Milliken. In exchange for airing the story of his daughter's death at Milliken's hands, Kelly asked for a presidential pardon for his son, who was on death row. However, Kelly disappeared under suspicious circumstances before Sherry had a chance to set up the pardon.

Tony Almeida
Between Day 3 and Day 4, Tony Almeida was convicted of treason for aiding the terrorist Stephen Saunders when Saunders had Tony's wife Michelle Dessler hostage. Before leaving office, President David Palmer granted Tony a presidential pardon, apparently following a request by their mutual friend Jack Bauer.

Behrooz and Dina Araz
Dina and Behrooz Araz were granted immunity during Day 4 in return for help finding Habib Marwan. Dina was shot by her husband and Behrooz was forced to go and get medical aid. While he was gone, CTU captured Dina and offered her and her son's freedom if she helped them.

Behrooz was captured by his father whilst getting help and was held hostage. Dina threatened to end their agreement if CTU did not rescue her son. She said that she believed in their cause but was doing what was right for her son.

When Dina helped in an undercover operation, as part of the pardon, her cover was blown and she was killed.

Behrooz was traded for Jack Bauer in an attempt to keep CTU from learning of the death of the Air Force pilot killed to give Mitch Anderson access to the Stealth fighter. Behrooz's final whereabouts was never revealed on screen.

Mandy
When she was captured at the end of Day 4, Mandy was offered a full pardon (for all crimes, present or past) in exchange for revealing Habib Marwan's location.

One complication was former President David Palmer, who was helping out during the day. Mandy was the person who almost killed him at the end of Day 2, and she would be pardoned for that crime as well. Palmer nevertheless advised President Charles Logan to go ahead with the deal, considering the gravity of Marwan's attack on Los Angeles with a nuclear weapon. After Mandy's lawyer, Todd Richards, assured her everything was in order, she gave up the location and was presumably released at a later date.

Jacob Rossler
On Day 5, Rossler was supposed to set up a meeting with Ivan Erwich to arm 20 nerve gas canisters, but CTU got to Rossler first. In exchange for his help in locating and capturing Erwich, Rossler demanded immunity for all his crimes, all of his money, transport to a foreign country of his choice, and his 15-year-old sex slave. Lynn McGill agreed to the terms, but the girl shot Rossler before he had a chance to collect.

Collette Stenger
During Day 5, Collette Stenger was granted immunity for promising to reveal the source of the blueprints to CTU. However, she lost her immunity when Bauer discovered she had lied about her source in an attempt to get Jack off the trail.

Hamri al-Assad
After it was discovered that Hamri al-Assad wished to renounce terrorism and bring his organization to participate in peaceful negotiations, he was pardoned by President Wayne Palmer in exchange for his assistance in tracking down Abu Fayed, who framed Assad for being responsible for numerous terrorist attacks around the country. The pardon angered Curtis Manning who threatened to kill Assad, but who was shot by Jack Bauer to prevent him from doing so.