Police need to check which tourists did not have their keys to their apartments at around 8.30pm - 9pm that evening, for example, were any of these tourists staying in apartment block 5?
He normally finished work around that time (8.30pm) and at 9pm he was making a call to his wife, to tell her he was going to be late home!
That's two important times, (8.30pm) being when Kate and Gerry McCann left their apartment 5a, that same evening, and (9pm) was around the time Gerry McCann went to do the first check of the apartment!
He must have had hold of the security keys at this time, to let tourists into their apartments!