He said 'make hay while the sun shines' and started working immediately.

This is the most difficult case I have ever faced.

He got involved in a love affair.

The Tiananmen Square incident is an important event in Chinese history.

The Marco Polo Bridge Incident was the trigger for the Sino-Japanese War.

He is known as an expert in criminal investigation.

He is known as an excellent criminal investigator.

He cooperated with the police as part of a sting operation.

I went to the police station yesterday.

Police dogs are very effective in tracking criminals.