Think of it in the present tense for a moment. We wouldn't say "I confess to kill", we'd say "I confess to killing". Therefore, the correct form in the past tense is "I confess to having killed", not "to have killed"; if you wanted to use "have killed", you'd have to supply a subject for the verb, as in "I confess I have killed". However, the sentence "He confessed to have killed" would be perfectly well understood even if it is sloppy English.@Thomas1
I don't think that "he confessed to have killed." is wrong. Isn't it possible to use it like some other verbs such as "believe" & "claim"?
He claims to have been discriminated against.
We believed him to have been wrongly accused by them.
Quite probably, Wormhole. News sites are written by journalists who are under pressure to publish their stories as quickly as possible - preferably before their competitors. The journalists' grammar is usually fairly good, but by no means perfect, and one can often spot minor mistakes.@panjandrum
So you are saying that the use of " I confess to have killed..." is not correct because "to", which is a preposition here as you've said, must be followed by a noun or noun phrase. I encountered the usage I have given above in some of the news websites, and they've made me confused.