On the 10th anniversary of the Washington sniper murders, killer Lee Boyd Malvo says that the devastated reaction of a victim's husband had made him feel like scum.
The 27-year-old urged the families of victims to try to forget about him and his partner, John Allen Muhammad, so they can get on with their lives.
Tuesday marks a decade since the start of the pair's deadly rampage.
They were linked to 27 shootings, including 10 fatal attacks in the Washington area over 23 days.
Malvo, who was 17 at the time, said the look on the face of victim Linda Franklin's husband when she was shot stood out in his memory of the killing spree.
Muhammad killed Franklin, a 47-year-old FBI analyst, as she and her husband Ted loaded goods at a Home Depot store in Falls Church, Virginia.
Malvo, using binoculars, acted as a spotter.
He told The Washington Post: "It is the worst sort of pain I have ever seen in my life.
"Words do not possess the depth in which to fully convey that emotion and what I felt when I saw it... you feel like the worst piece of scum on the planet."
Malvo is serving a life sentence without parole at a Virginia prison for killing Franklin.
Muhammad, a Gulf War veteran, was executed in Virginia in 2009.
The attacks terrorised the US capital. People were shot at random in car parks and at shops. A 13-year-old boy was wounded outside his school.
Malvo and Muhammad carried out their attacks with a rifle fired from the boot of a Chevy Caprice car until authorities tracked them down at a service station in Maryland.
In the interview, Malvo repeated assertions that his older partner manipulated him, but added: "I was a monster. If you look up the definition, that's what I was."