Problem Understanding the 経つ Verb


So I came across this sentence in a textbook:

> 家の近くで殺人事件が起きて１か月経つが、いまだに犯人は見つかっていない。

I think the sentence is supposed to mean 'Since the murder occurred near my
house, a month has passed, but the criminal has yet to been found.'.

Same for the following sentence:

> 彼がここへ来てから一年が経つ。(Which I interpret as 'a year has passed since he came
> here'.)

The thing I'm getting stuck on is, as 経つ is a verb in its non-past form
describing the 'passing of time', doesn't it convey the meaning of a
habit/tendency or future passing of time? Intuitively I would have guessed
経った(passed) to be used instead of 経つ in the sentence.

Also, is the verb 経つ durative (referring to the action of the passing of
time), or is it a punctual verb (referring to the instant a specified window
of time has passed if that makes sense). If it's a punctual verb, 経っている would
be more appropriate right?




I don't have very grammatical explanations, but let's focus on the second
sentence.

Suppose he arrived 10 July 2020. Today it is 10 July 2021.

Then '彼がここへ来てから一年が経つ' can be used yesterday (09 July) or today or tomorrow (11
July). Or in past (say a week ago) or in future (a week later).

'..経った/経っている' on the other hand can be used today or after, not yesterday. (I
mean, strictly speaking the sentence '彼がここへ来て一年が経った/経っている' is false on 09 July
2021)

In English, I believe 'it's been a year since' and 'it is a year since' are
both acceptable (the latter being probably less formal). I guess ' _it is a
year since he came here'_ is not (particularly) considered to be false on 09
July 2021 in the above setting while ' _it's been a year..._ ' is technically
false on that day. I thought the difference 経つ/経った might be similar.

If the last paragraph is correct, then the simple explanation would be that
the present tense includes some time in near-past and in near-future in both
English and Japanese.

**Edit: some more comments**

Of course, 経った/経っている can be used in both of your examples, and that might be
more precise. But the present tense here just refers to a fuzzy time period
around now.

There is also something to do with the length of time concerned.

Suppose you poured hot water into cup noodle and are waiting for 3 mins. Then,

  * '3分経つ' can be used only slightly before 2'59''

  * '3分経った' is used after 3'00''.

This is probably because the length of time is too short to accommodate the
past and future.




I don't have very grammatical explanations, but let's focus on the second
sentence.

Suppose he arrived 10 July 2020. Today it is 10 July 2021.

Then '彼がここへ来てから一年が経つ' can be used yesterday (09 July) or today or tomorrow (11
July). Or in past (say a week ago) or in future (a week later).

'..経った/経っている' on the other hand can be used today or after, not yesterday. (I
mean, strictly speaking the sentence '彼がここへ来て一年が経った/経っている' is false on 09 July
2021)

In English, I believe 'it's been a year since' and 'it is a year since' are
both acceptable (the latter being probably less formal). I guess ' _it is a
year since he came here'_ is not (particularly) considered to be false on 09
July 2021 in the above setting while ' _it's been a year..._ ' is technically
false on that day. I thought the difference 経つ/経った might be similar.

If the last paragraph is correct, then the simple explanation would be that
the present tense includes some time in near-past and in near-future in both
English and Japanese.

**Edit: some more comments**

Of course, 経った/経っている can be used in both of your examples, and that might be
more precise. But the present tense here just refers to a fuzzy time period
around now.

There is also something to do with the length of time concerned.

Suppose you poured hot water into cup noodle and are waiting for 3 mins. Then,

  * '3分経つ' can be used only slightly before 2'59''

  * '3分経った' is used after 3'00''.

This is probably because the length of time is too short to accommodate the
past and future.

