Although he had been drinking, he would have had a reason for leaving the pub and heading to wherever it is that he went. I don’t think he has left the pub to simply make a call in private (by going outside where there is less noise), or to look for an ATM or go for some food. I think he had a specific reason for leaving. Am I right in thinking that the Police will have tried to retrieve data from his number such as last calls, messages and whether or not he accessed any websites from his phone that night before he left the pub.