FIR of theft can be filed

The legal heirs have two options, first one to lodge a complaint against the mischievous thoughts of the custodian to fraudulently usurp the assets of the deceased and cheating the legal heirs.

The second option to file a succession certificate before court with the pleadings to direct the custodian to produce the original relevant papers before court to ascertain court fees and stamp duty to issue succession certificate in favour of the successors in interest to succeed to the assets left behind by the deceased.

Section 378 of Indian Penal Code 1860 defines "theft" as under:

"Whoever, intending to take dishonestly any movable property out of the possession of any person without that person's consent, moves that property in order to such taking, is said to commit theft."

Explanation 1.—A thing so long as it is attached to the earth, not being movable property, is not the subject of theft; but it becomes capable of being the subject of theft as soon as it is severed from the earth.
Explanation 2.—A moving effected by the same act which effects the severance may be a theft.
Explanation 3.—A person is said to cause a thing to move by removing an obstacle which prevented it from moving or by separating it from any other thing, as well as by actually moving it.
Explanation 4.—A person, who by any means causes an animal to move, is said to move that animal, and to move everything which, in consequence of the motion so caused, is moved by that animal.
Explanation 5.—The consent mentioned in the definition may be express or implied, and may be given either by the person in possession, or by any person having for that purpose authority either express or implied.
Accordingly instant case do not fall under section 378 of IPC i.e, 'THEFT" 

It will attract Section 406 IPC for criminal breech of trust.

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