With reference to this question Collective noun "police" — singular or plural? and as per my understanding Police is always plural. But I got shocked after seeing police used as singular noun.

Two days after the death of the 23-year-old gangrape victim, Delhi Police on Monday said it has finalised around 1,000-page chargesheet in connection with the incident and plans to submit it in court on Thursday.

I can't figure out why they have used police as singular. Also its one of the prominent newspaper in India. I doubt on myself about its usage. Could any one elucidate it further ?