|Portrayed by||Bonnie Root|
|First Appearance||The Key|
Alexandra Thomas was an Assistant District Attorney in Philadelphia who often worked closely with the Philly PD's Homicide Unit. She eventually entered into a relationship with Homicide Detective Scotty Valens in 2007, which ended in 2008.
Alex first approached Scotty in the fall of 2006, while building a case against Fitzpatrick, a boxing coach alleged to have molested several young boys for several years. She noted that Scotty's older brother Mike Valens was among his students. After the sole witness against Fitzpatrick committed suicide, she urged Scotty to have his brother to come forward. Scotty was reluctant to get his brother involved, but eventually convinced Mike to testify against Fitzpatrick.
Months later, Alex assisted Homicide detectives when Mitch Hathaway threw registered sex offender Harold Dixon off the roof of a building to his death, leaving a note promising to kill another sex offender everyday until the 1987 rape and murder of his six year old son Clayton Hathaway was solved. Alex explained that Hathaway had been arrested and convicted for his son's murder, but had been released in 2007 after evidence against him was found to be contaminated.
Alex objected to Scotty's ambivalent attitude to Hathaway killing people, even sex offenders. She was further incensed when Hathaway killed another sex offender, Ernie Grabowski, shortly after being questioned by Scotty and Nick Vera about Clayton's murder, without the two informing him of a possible threat to his life. Eventually both Hathaway and his son's killer Cliff Burrell were apprehended, though not before Hathaway nearly threw Burrell to his death as well, due to Scotty letting slip a piece of information in a phone conversation, unwittingly allowing Hathaway to deduce the identity of his son's killer.
Alex later briefed detectives on an FBI case being built against a human trafficking crime boss known only as "Nachalnik". The body of a Jane Doe believed to be a victim of Nachalnik had recently been found in the river and Alex asked about any possibly relevant cases that may assist the FBI. This led to detectives reopening the 2005 murder case of Mike Chulaski. When Kiril, an employee of Nachalnik's was apprehended as a suspect in Mike's murder, Alex noted her office was willing to make a deal with Kiril in return for him identifying Nachalnik, even if he had killed Mike. Scotty objected to making any sort of deal with a murderer, but Alex was unmoved, reminding him that he "screwed up" on the Hathaway case, and urging him not to do the same again. Scotty retorted that it bothered her that he could handle her. Eventually, both Nachalnik, and Mike's actual killer, Kateryna Yechenko, were apprehended.
- It's unclear if Alex did make a deal with Kiril to testify against Nachalnik, though she later was seen at his cell.
Alex later asked Scotty and his partner Detective Lilly Rush to interview shooting victim Kim Jacobi, who had recently emerged from a coma. Kim had been the sole survivor of a 2006 shooting that had killed her parents Adam and Emily Jacobi and brother Stewart Jacobi, and it was assumed Adam had shot his family before turning the gun on himself. Kim's memories of the night were cloudy, but she indicated someone else had shot her family. Sometime later, the shooter, an obsessed admirer of Kim named Ed Marteson would smuggle a gun into Homicide and take Kim and several detectives hostages. Against orders, Scotty broke perimeter, entered the building and managed to shoot and kill Ed, though not before Ed shot and badly wounded Lilly. Despite their past arguments, Alex would console Scotty while his partner was treated in the hospital.
Weeks later, Scotty was investigated by Internal Affairs officer Ari Gordon about disobeying orders during the hostage crisis, as well as his actions during the the Hatahway case. Curious to know how Gordon had learned of the latter information, Scotty discovered Alex had been speaking with Gordon. He later confronted her and the two argued, though their anger soon gave way to passion and two would begin a quiet affair.
After weeks of sneaking around, Scotty expressed an interest in seeing Alex openly, though both were tentative about this. Soon after, Alex would assist Homicide in searching for a serial bomber, whose latest bomb had maimed John Wojciechowski at a local gym. At Vera's request, Alex subpoenaed a purchasing order from the supplier from whom the bomber had ordered his parts. Providing detectives with the name "Carl Baxter", she also provided them with a search warrant for Baxter's residence. It was later learned that the bomber, whose real name was Alessandro Rossilini, had in fact been targeting a man named Luke Ross. Detectives kept this information to themselves to prevent another attack on Ross.
Unfortunately, the DA's office soon brought FBI into the investigation and issued a press release naming Ross as the bomber's intended target. Scotty angrily confronted Alex about this, telling her the FBI only takes information, never sharing it, and that her office had put Ross in danger. Alex coolly told him her job was to catch Rossilini and that Ross was not her problem. Scotty told her if the bomber killed Ross now, his blood would be on her hands.
Scotty's fears would prove justified when Rossilini (who was discovered to be Luke Ross' estranged older brother) planted another bomb in a music box at the school of Ross' daughter Mia Ross. Mia brought the music box home with her Ross' wife Beth Ross picked her up, and only the timely intervention of Vera and Detective Kat Miller prevented them from being killed when the bomb went off.
Alex arrived at the Ross' damaged home and appeared visibly troubled at the sight. Scotty, disgusted that her actions had nearly led to the death of Ross' family, simply gave her a cold look and turned away.
Scotty and Alex's relationship apparently ended after this, and months later, Scotty would being dating lab technician Frankie Rafferty.