Investigámos a ameaça ontem.

In European Portuguese, investigámos is the simple past form (pretérito perfeito simples) meaning we investigated.

The accent is important because it helps distinguish it from investigamos, which is the present tense form:

• investigámos = we investigated
• investigamos = we investigate

This is a useful spelling distinction in European Portuguese, especially with regular -ar verbs.

Portuguese often omits the subject pronoun because the verb ending already shows who is doing the action.

Here, the ending -mos tells you the subject is we.

So both of these are correct:

• Investigámos a ameaça ontem.
• Nós investigámos a ameaça ontem.

The version without nós is very normal and natural.

Here, a is the feminine singular definite article, so it means the.

• a = the for feminine singular nouns
• ameaça is a feminine noun

So:

• a ameaça = the threat

If the noun were masculine singular, you would usually see o instead.

Because this sentence is talking about a specific threat, not the idea of threat in general.

In Portuguese, when a specific countable thing is meant, the article is usually used:

• a ameaça = the threat
• ameaças = threats
• bare ameaça here would sound incomplete or unnatural in normal usage

So a ameaça is the natural form for the threat.

Investigámos is the simple past: a completed action.

It fits well with ontem because the action is seen as finished:

• Investigámos a ameaça ontem. = completed yesterday

Investigávamos is the imperfect, which usually suggests:

• an ongoing action in the past
• a repeated/habitual action
• background information

For example:

• Investigávamos a ameaça quando recebemos novas informações.
  = We were investigating the threat when we received new information.

So investigámos is the right choice for one completed action yesterday.

Yes. Portuguese word order is fairly flexible with time expressions like ontem.

All of these are possible:

• Investigámos a ameaça ontem.
• Ontem investigámos a ameaça.

The version with ontem at the end sounds very natural and neutral. Putting ontem first gives it a little more emphasis.

The ç is pronounced like s.

So in ameaça, the ç gives an s sound before a. Without the cedilla, c before a would normally sound like k.

A few useful pronunciation points:

• ameaça is split as a-me-a-ça
• the vowels in me-a are in separate syllables
• ç = s

So the most important thing to remember is that ameaça does not sound like it has a k sound before the final a.

No contraction happens here.

That is because the first a is the article (the) and the second a is simply the first letter of the noun ameaça.

So:

• a ameaça = article + noun

Portuguese contractions usually happen when a preposition combines with an article, for example:

• de + a = da
• em + a = na
• a + a = à

But in a ameaça, there is no preposition to contract, so it stays as a ameaça.

Yes. Investigar is a regular -ar verb.

That means its forms follow the normal pattern for -ar verbs. In this sentence:

• infinitive: investigar
• stem: investig-
• ending for we in the simple past: -ámos

So:

• investigámos = we investigated

This same pattern appears in many other regular -ar verbs in European Portuguese:

• falámos = we spoke
• estudámos = we studied
• comprámos = we bought