The fundamental principle of Anglo-Saxon law is that even if thousands of guilty people escape, no innocent person should be punished. The insistence on the “proof beyond reasonable doubt” is the fall out of this principle. It is for this reason the proof of motive is insisted upon. However in this era of codified/defined offences, in the face of direct evidence, many a time motive takes back seat and convictions are made even if the prosecution is not able to prove the motive. See:

It is an admitted fact that Abdulas (A-2) caused spear blow in the vital part of Nisar Ahmad, which resulted in his instantaneous death. The nature of the injury caused by the weapon used on the vital part of the body, be it noted against an unarmed person negates any just plea for right to self defence. Here we have to point out that it is very well established by a catena of cases of this Court that when the occurrence was spoken to by eye-witness and the same was supported by Medical Report, it will not be necessary to investigate the motive behind such commission of offence. In other words, where a murderous assault has been established by clear ocular evidence, motive pales into insignificance as rightly found by the High Court. [(Baitullah vs State Of U.P, AIR 1997 SC 3946, 1997 (2) ALD Cri 666, 1997 (3) CTC 223 (on 17 October, 1997)]

In yet another case of clear direct evidence it was observed:

The evidence in the present case is so clear to show that these four persons committed the murder of the eight boys that we think it unnecessary to speculate about the motive which induced them to murder the eight boys who had done no harm. Whether it was sadistic pleasure or the fear of discovery of robbory, or anything else, the fact remains proved by overwhelming evidence that these four did actually commit the murder of the eight innocent boys. [Nand Kumar & Others vs State Of Rajasthan on 3 May, 1962]

In another case of Delhi High court refused to convict the accused, without any proof of motive, where the ocular evidence or the version of eyewitnesses was contradictory inter se as well as with medical evidence. (See Parmersh Kumar vs. State Crl. Appeal No 52 of 1993 decided on 06.03.2009followed in Jawahar vs. State, Crl Appeal No. 338 of 1997)

It appears that in case of circumstantial evidence insistence of proof is invariable rule and absence of proof of motive is rare exception.

Some More material: Tarseem Kumar versus Delhi Administration (1994 (Suppl. 3) SCC 367), Jamna and Others versus State of U.P. (1994 (Suppl. 1) SCC 185) and Kuriakose and Another versus State of Kerala (1994 (Suppl. 1) SCC 602).