Investigators told The San Diego Union-Tribune that Kiel had just left the home of linebacker Stephen Cooper July 4 when his car slammed into a wall about a mile away.
"We suspect he was driving at a very high rate of speed," police Sgt. Jeff Fellows told the newspaper.
Previous reports have said other guests tried to take Kiel's keys from him at the party. The newspaper said investigators were also looking into witness reports that Kiel was driving on the wrong side of the road when the accident occurred.
The Chargers cut Kiel in 2006 after he was arrested for shipping bottles of prescription medicine to an acquaintance in Texas.