Shembo's quick departure showed that the Falcons are still sensitive to animal abuse eight years after star quarterback Michael Vick served an 18-month federal prison sentence for running a dogfighting ring.
The charges against Vick caused a national uproar over dogfighting in 2007. That same year, Falcons defensive tackle Jonathan Babineaux, who is still with the team, was arrested for his alleged involvement in the death of his girlfriend's dog, but the charges were later dropped.
"Professional athletes are role models in our society, so it's critical for NFL teams to send their players the message that bullying and abusing anyone is unacceptable," Ingrid E. Newkirk, the president of People for the Ethical Treatment of Animals, wrote in the letter.
"We would again suggest, as we have in the past, that requiring all athletes to receive empathy training would give them more self-respect and positive guidelines for how to behave toward others. Former Atlanta Falcons quarterback Michael Vick completed our eight-hour basic class in empathy and animal protection at PETA's headquarters following his arrest for dogfighting crimes. Perhaps if he had taken such a course earlier, he might never have caused such suffering and brought disrepute to his team and the league."
On Tuesday, coach Dan Quinn said he believed the team made the right decision to cut ties immediately with Shembo.
"We felt it was best for us to handle the things we could on the field and then also for him to handle the things he needed to do off the field," Quinn said Tuesday after the team's workout.
A report from the Gwinnett sheriff's office said that Shembo killed the tiny Yorkshire Terrier on April 15. Quinn and the Falcons didn't learn of the incident until last Friday when the player was arrested. Jail records show that Shembo posted a $16,700 bond.
The Falcons drafted Shembo out of Notre Dame last year. He played in 16 games with three starts, but there were some off-the-field questions about Shembo coming out of college.
General manager Thomas Dimitroff selected Shembo despite an alleged sexual misconduct incident in 2010 -- the player's freshman season -- involving a St. Mary's College student who later killed herself.
Dimitroff said on draft day last year that the Falcons thought Shembo was worth the fourth-round pick the team used to select him.
"We're very, very aware of the seriousness of the incident, and obviously it's a sad situation for the young lady involved," Dimitroff said then. "We've done a lot of research on many levels from our security standpoint, and from all the research we did at Notre Dame, he was never charged, never suspended from the team or the school."
The Associated Press contributed to this report.
Falcons' Shembo arrested, cut
ESPN Falcons reporter Vaughn McClure discusses Atlanta's decision to cut linebacker Prince Shembo after he was arrested and charged with felony aggravated cruelty to an animal.