Это всё интересно. В общем я выбираю верить носителей русского языка, в том числе преподаватель языков.
Однако, мне не нравится весь разговор об убийстве! 
Да, я конечно согласен, но все носители не говорят то же самое. Вот то, что интересно.
Убийство не приятный пример.
I have an interesting (to me :)) book published in 1970 “A Grammar of Aspect: Usage and Meaning in the Russian Verb” by J Forsyth. Instead of defining what each aspect is, he is of the opinion that the best way to approach them is to define only the perfective viz. “a perfective verb expresses the action as a total event summed up with reference to a single specific juncture.” The imperfective is just the opposite 
He then goes on to explain, even with reference to ‘Aktionsarten’, over the following 350 pages what he means. I think the посмотрел/смотрел фильм dilemma happens to most students. I couldn’t understand why to use смотреть when I was talking about watching an entire film to the end.
I realise that this kind of book is probably of little help when speaking the language, and that native speakers don’t consult them, but … I just like reading them…
All books can be useful to a certain extent.
But I don’t think that this meaning about the Perfective Aspect in Russdian is true.
The MAIN basic aspect in Russian is IMPERFECTIVE aspect which expresses any actiion.
And the perfective aspect only helps to express the resultative separate actions in the Past and in the Future.
There are some exceptions, but for 95% it is its main predistination.
To paraphrase Douglas Adams, ‘‘Aspect is an illusion. Unmarked aspect doubly so’’.
Personally, I can’t see what exactly markedness defines when it comes to aspects. Moreover, from the practical point of view, the very idea that ‘‘the imperfective aspect is unmarked’’ may be highly misleading for learners (though it’s hard for me to judge of course).
Here’s the short video about aspects (not exactly about markedness, just to practice your listening): http://postnauka.ru/video/26225 (in Russian).
The idea is to explain when to use one aspect over another. It’s not about defining.
It’s an attempt to answer a common question among foreign learners.
Why does this form sound more natural in this context than another one, even though both are theoretically correct?
Examples are provided above.
Interchangeability of the aspects is a very relative thing, that’s why I recommend to be careful with it. The correct choice depends not only on the semantics of the verb, but also on the STYLISTICS of the sentence/context.
For example. Take two questions: ‘‘Ты брал деньги со стола?’’ (imperfective) and ‘‘Ты взял деньги со стола?’’ (perfective). Semantically (on their own) both mean the same thing – ‘‘Did you take the money from the table?’’ (or Have you taken…) – but they are used in different situations:
- ты брал? would be used in the situation like: ‘‘I had the money on the table and they are gone. Did you happen to take them?’’,
while 2) ты взял? is like: ''I left money on the table (to buy smth). Did you take them? = You haven’t forgotten to take them?
So, the imperfective aspect might be used when you are asking more general questions, while the perfective might be more specific in some contexts.
BUT when you shift the intonation from the verb to the pronoun they lose those distinctions and can be used interchangably, eg. : ТЫ взял деньги со стола?! = ТЫ брал деньги со стола?!! (YOU took those money?). In this case, there’s no difference between the two (though the perfective would be more common).
That’s the easiest example which came to my mind, stylistic distinctions may be even more complicated and difficult to explain.
In short, one aspect is chosen over another because of 1) the semantics of the verb; 2) stylistics of the given context.
Thank you for the information. I wasn’t aware of the effect of shifting the stress to the pronoun.