have killed three people in the past/in the past three years

[joham]

What does 'in the past' mean? Can 'in the past' equal 'once in the past' in this sentence?
'I have killed three people in the past.'
The book I was reading says this above sentence can only mean that there has been an occasion in the past on which I killed three people: the sentence cannot be used in answer to the question 'How many people have you ever killed / killed up to now?'

That means the above sentence doesn't equal sentences like 'I have killed three people in the past three years'.
And how about the sentence 'The backroom boys have decided too many things in the past. Their day is over.'?

[Gillnetter]

What does 'in the past' mean? Can 'in the past' equal 'once in the past' in this sentence?
'I have killed three people in the past.'
The book I was reading says this above sentence can only mean that there has been an occasion in the past on which I killed three people: the sentence cannot be used in answer to the question 'How many people have you ever killed / killed up to now?' This is not correct.

That means the above sentence doesn't equal sentences like 'I have killed three people in the past three years'. No, it doesn't equal the first sentence because it is more definite as to time.
And how about the sentence 'The backroom boys have decided too many things in the past. Their day is over.'?

In the past = Sometime before this time

I have killed three people in the past = I may have killed one person in 1946, one person in 1976 and one person last week. We don't know when these three people were killed, we only know that the killings happened sometime in the past.