Could the police cruisers of the future be purely electric vehicles? Most likely. But right now, the idea is a bit out of reach.
Los Angeles Police Department has been using 2 Tesla Model S cars to see if they would fit in as police cruisers. Something tells me the Insane Mode might come in handy there. After one year of testing, they believe it isn't feasible currently. Between the cost of the cars and lack of charging stations it's difficult for them to see it working.
The S Model is expensive; it is a Tesla after all. Coming in at $100k, it's about $30k more than LAPD's current Ford Explorer.
Not only that, the charging stations are hard to come by. If police needed to respond in a natural disaster, it could be difficult if the charging stations have been knocked out.
LAPD is looking into their future with electric vehicles, and hopes that in the next 5 to 6 years the market is more affordable, and charging stations more available to help them make this eco-friendly move.