Question

When the cops arrived the crook ran outside? change into formal sentence

Answer 1

The crook ran outside as soon as the cops arrived.

Answer 2

At the time, when the cops arrived, the crook ran outside the home. In this sentence the meaning has been kept the same.

It is changed into a formal sentence according to the rule of English grammar.

The use of tense, subject verb agreement etc. has been kept consistent, meaningful, and grammatically correct.

The original meaning of the sentence is well maintained.