WASHINGTON -- Animal control investigators in Washington told Channel 2 Action News Wednesday that they've received tips linking Atlanta Falcons quarterback Michael Vick to dog fighting for years.

An official with the U.S. Humane Society, the nation's largest animal protection group, told Channel 2’s Scott MacFarlane that he's been hearing reports from tipsters about Vick and dog fighting since 2004.

“Some of these calls have been from people who claim to have knowledge about Michael Vick, but it was never enough where we could ID where the dogs were and make a case against Vick,” said Humane Society investigator John Goodwin.

The Humane Society is urging Virginia investigators to do another search of the Surry County property formerly owned by Vick.

Officials found more 60 dogs when the property was searched last month.

Animal control officers now suspect there are 30 dogs buried somewhere outside the home.

A police affidavit obtained by Channel 2 Action News also says they have “reliable sources of information that at least seven of those pit bulls were killed and buried just two days before the first police raid in April.”

“This affidavit that was filed has highly detailed information about the exact number of dogs buried on that property and when some of them were killed, said Goodwin.

“That tells me that someone has good information and that could be very bad news for Michael Vick."

The Humane Society offers $2,500 rewards for tips that lead to prosecution.