We've learned hours before Lindsay allegedly battered a Betty Ford staffer ... she was hanging out in a hotel room with Adam Case, a fellow Betty Ford patient who spent a lot of time with LiLo over the last few months. In fact, Case took Lindsay back to her place when she was confronted by B.F. staffer Dawn Holland and saw the whole altercation.
Our sources say Palm Desert cops are convinced ... Lindsay was drinking in the hotel room, and they think Case could be their star witness to prove it. They also believe Case saw Lindsay attack Holland.
Cops got a statement from Case the night of the incident, and he sided squarely with Lindsay. Dissatisfied, cops went back to Case the next day and grilled him again, to no avail.
But that wasn't the end. Days later Palm Desert cops went to Case yet again and interrogated him over what Lindsay did in the hotel room -- specifically, whether she consumed alcohol. Case said he never saw her take a drink. Cops pressed Case to get a copy of his hotel bill, but he refused.
As for what happened in the hotel room, Case says Lindsay spent an hour-and-a-half dying her hair, then hung out with him and a few other friends.