LE didn't charge him at the time, they only searched his home, IIRC. Once he disappeared, LE didn't say anything. It wasn't until after he was declared dead that they released the information.
JMO, that meant they had plenty of time in the intervening year or so to conduct a full investigation and conclude there was enough evidence against him. They would verify the information through analysis of files on his phone, IP account, maybe even GPS, travel and work schedules, etc. It was probably part of a much wider investigation. JMO