Tony would not realise that the forensic team had found no trace of Terry - not even the tiniest body part in or around the remains of his coffin or elsewhere in the church. It may well have been his funeral, but he surely wasn't at it. The police didn't intend Tony to know this before he'd had a chance to 'help them with their enquiries'. Assuming he survived.
The forensics team were able to establish the former contents of the coffin - a large explosive device and mobile network triggering device. Realism was ensured by a bodyweight of lead lining beneath.