"Do not cross the limit. Do not hurt anyone's religious belief," Inspector General of Police AKM Shahidul Hoque said.
The "freethinkers" should keep in mind that hurting someone's religious sentiment is a criminal offence, Bdnews quoted Hoque as saying.
On the killing of blogger Niloy Chakrabarty Neel, Hoque said police were investigating it "with top priority".
Neel was hacked to death by four assailants inside his flat in the capital's Goran area on Friday.
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Meanwhile, a team of the Federal Bureau of Investigation (FBI) of the US met detectives in Dhaka yesterday.
The FBI team wanted to share their technical expertise with local detectives in the investigation, Deputy Commissioner (Detective Branch) Mahbub Alam of Dhaka Metropolitan Police told reporters after the meeting.
They also talked about the progress of investigation into the murder of secular writer Avijit Roy, he added.
Replying to a query, Mahbub said the bloodstained T-shirt found at the crime scene was left behind by the killers. "It is a vital piece of evidence."
Industries Minister Amir Hossain Amu yesterday said the blogger killings had political motive behind them.
"We strongly believe that these are planned murders. Those who wanted to destabilise the country with violence are behind the killings," said Amu.
Apart from Neel, other bloggers killed this year are Avijit Roy, Washiqur Rahman and Ananta Bijoy Das.