Ex-NFL Player -- Mistress Murders Wife ... Cops Say (Update)

3:11 PM PT -- The Clayton County P.D. tells us ... Buster was at work at the time of the kidnapping and was unharmed in the incident.

We're also told Buster's mistress had gone to Buster's workplace right BEFORE the kidnapping -- and told him she was MAD that Buster and his wife were going on a vacation together.

Cops say Buster insists he had no idea Brown was homicidal -- and didn't think the situation would escalate, which is why he did not call police.

Barnett is not a suspect or a person of interest.

The mistress of a former NFL player went berserk in Georgia -- kidnapping the man's wife and then killing her and herself after a high speed car chase ... this according to police.

Cops say the killer was the mistress of Buster Barnett -- a former tight end for the Buffalo Bills from '81 to '84.

Barnett's mistress, Lisa Brown, kidnapped Buster's wife, Sandra Barnett, and sped off in a Dodge Durango ... officials told 11Alive.com.

The Durango was spotted by police and a chase ensued -- through Georgia and into Alabama ... until the car suddenly stopped -- and that's when cops say Brown opened fire on Barnett and then herself.

No word if Buster was harmed in the incident.