During the subsequent interview, Kelly appeared 'proud' of the attack and also confessed to the 18 Tube murders, MailOnline reported.
Former Met detective Mr Platt added: '[Kelly] was loaded with adrenaline, he was loaded with testosterone, he couldn't stop talking and he came out and started telling everything.
'We actually started to think it was b*******. There was a certain caution in some respects.'
Mr Platt was assigned to investigate his claims, and realised there were several reported suicides on the Tube where Kelly had been at the scene.
'What immediately came to notice was that there were a number of people who jumped off the platform into the Northern Line,' he said. 'But what especially smacked you in the face was every time someone jumped on the track ... Kelly was next to him.'
Despite the seriousness of the allegations, police decided not to brief the Press or public due to concerns passengers would be too scared to ride the Tube. Mr Platt told a newspaper yesterday: 'It was a cover-up. Think about it, the police don't want it getting out - there would be mass panic. They didn't want people knowing a serial killer got away with pushing innocent people on to the tracks, they'd be afraid it could happen again.'
Mr Platt details the claims in his book, The London Underground Serial Killer.
Kelly was jailed for life for murdering Boyd, and Hector Fisher - another vagrant who was found stabbed in a South London graveyard in 1975. Although Kelly was questioned over Mr Fisher's death at the time, it was not until 1984 that he was convicted.
Another homeless man, Maurice Weighly, was found murdered in Soho in 1977 - but Kelly was cleared after it was revealed the key witness had been extremely drunk.
Kelly was also charged with attempted murder in 1982 after an elderly man was pushed on to train tracks in Kensington, but he was found not guilty due to a lack of evidence.
A British Transport Police spokesman said: 'We are aware of the claims ... but given the passage of time since they are alleged to have been committed these would prove difficult to substantiate without further evidence. We would invite Mr Platt to submit any information he has on these matters.'
- Daily Mail