In the Early Cuts series, he was a former sniper in the Marines who murdered three innocent children, before being discharged. However, it is revealed via an official website that in the Showtime series, Alex began murdering people after he was discharged, targeting innocent victims back in the states, killing four people with gunshots. He is one of Dexter Morgan's earlier kills and also the one that inspired him to make trophies out of blood slides.
Alex is a muscular, African-American male with a mustache and a little bit of a beard. He has relatively short black hair and a tattoo from the Marines on his right arm. He wears a variety of different clothes, from hunting attire to tight-fitting muscle-T's and even a cap.
Alex has a demented Dark Passenger of his own, claimed as Dark Urges. He desires nothing more than to kill innocent, defenseless beings such as children. He lives his life this way, having a hardened exterior personality that pushes a lot of people away...and then uses the cover of military to kill children, which infuriates him once he is sent home. However, he has a very cowardly personality at death...saying everything and anything he can muster to try and not die...which doesn't work in Dexter's case.
It is not revealed what his motivation for killing four innocent people in the Showtimes series was, but since it is mentioned that none of his victims (with the exception of a 17-year-old girl) were children, his personality could not have been exactly the same as his Early Cuts counterpart, so he may have had some other motivation other than simply satisfying a homicidal urge to kill. In the flashback of Alex's death in the Showtimes series, he also did not seem to show the same level of fear that his Early Cuts counterpart did; he was not begging for his life, instead admitting to his crimes and rather angrily asking Dexter if that was what he wanted to hear-though he certainly showed a certain degree of fear as he said this.
Timmons had been a hunter since he was young, developing a fondness for killing. He later became a U.S. Marine Corps sniper, allowing him to kill in the open while masking it as warfighting. While fighting in Iraq during the Gulf War, his impulse to kill eventually overcame him, causing him to shoot and kill three civilian children. He got off with a slap on the wrist, being discharged from the Corps.Dexter first approached him at a gun range which Timmons often practiced at. He then pretended that his car had broken down and asked Timmons for assistance. While he was distracted, Dexter sedated him, abducted him and killed him in his home with a Marine Corps combat knife.
When the Ice Truck Killer brought Valerie Castillo, Dexter's last victim, back from the ocean, a police investigation was started and Dexter decided to eliminate any evidence that might implicate him. Dexter threw all of his killing tools in the ocean and was about to do the same to his blood slides. Before doing this he went through his blood slides and remembered some of his victims. Alex was the first victim that Dexter remembered. Like most of Dexter's victims, Alex was wrapped in plastic wrap. Before his death Alex admitted that he had committed the crimes which brought him there.
Alex Timmons is responsible for the deaths of at least three children over in Iraq, who knows how many other countless kids he has murdered along with them. Apart from the murders however, he has killed for the military, most likely having a body count of over 50 to a hundred men and women.
However this information is not mentioned for the Showtime Series, instead Alex killed four innocent people in the states and none of them were children (one was 17 but the rest were adults).