If police try to arrest somebody they must have arrest warrant to arrest him. There are some grounds where police can arrest a person without warrant. Under section 54 of Cr.P.C. Of Bangladesh 1898 and section 41 of Cr.P.C. Of India 1973 police can arrest without warrant if they found one of those ground below ---
Section 54 : Police may arrest without warrant
complaint has been made credible of has been , or a reasonable suspicion exists of his having
been so concerned.
"Unless there is an information or a reasonable suspicion that a person had been concerned
in a cognizable offense the arrest is unwarranted.” -------- 44 CWN 502
"when a person concerned in a cognizable offense the police can arrest him without warrant
under sec 54 of the Code,” --------------- Abdur Rahaman Vs The State 29 DLR (SC) 256
“An arrest for procession of implements of house breaking can only be made when the police have received some definite information about it. A arrest cannot be made when there is no definite information and it cannot be justified on the ground that on search such on implement happened to be founded in the procession of the person arrested.”
------- Emperor Vs Abdul Halim AIR 1942
"Proper publication of proclamation is necessary to arrest a proclaimed offender. “
------AIR 1936 Pat 249., 37 Cr.L.J. 318
" The procession of stolen property must be recent and exclusive.” ----------- 8 WR 28
Md. Shahnewaz Zwaki Advocate The Supreme Court of Bangladesh (High Court Division).