If there is ever a suspicion that a "one under" was a deliberate act
by another party, it's almost always a much longer job - entire
station closed, scene of crime officers called in etc. etc.
Sounds to me that, under the circumstances, it didn't take an
unreasonable amount of time. And let's face it, if that was your
loved one under the train, you'd want them to ensure that no evidence
was missed even if it did mean more inconvenience to other people.