In this instance, apparently there were multiple calls to the police, Brown virtually admitting it by saying it was just a moment that happened, his wife having gone to neighbors including Matt Hasselbeck and Chris Spencer during other instances, and Brown undergoing therapy for abusive behavior. Probably more than enough for the league to act on.
The NFL, with its vaunted security staff of former FBI agents, is not as adept as the daily news paper at getting records. Which means they aren't actually trying at all:
Upon news of Brown’s suspension, the New York Daily News quickly obtained police reports, a pair of 911 recordings on consecutive days and a lengthy statement from Brown’s wife (now divorced) to a detective and court official detailing 20 violent incidents spanning six years. Brown pushed his wife into a door when she was pregnant, once shoved her into a mirror and threatened her numerous times, according to her statement.
The NFL claimed that it obtained none of this information. The victim declined to speak to league investigators, and apparently Daily News reporters are better at obtaining court documents than the NFL’s army of super-sleuths.
Bud Adams told me the franchise he admired the most was the Kansas City Chiefs. Then he asked for more hookers and blow.