You don't understand the problem. If we encounter aliens, they would likely make a law to protect them. In the situation I came up with, this is their first encounter with us, and they would NOT be protected. You are very optimistic that they will be considered animals. For example they would have to live on organic matter. And they would have to have a spine to get more protection since living things with a spine are considered more valuable (Wirbeltiere).

GROK (And using all the Roman law principles on what German law is based):

Nullum crimen, nulla poena sine lege (Art. 103 Abs. 2 Grundgesetz + § 1 StGB) is the decisive wall that the prosecution would smash into in a real first-contact case under current German law. This principle has four sub-requirements (all must be fulfilled for a conviction):

Lex scripta – there must be a written statute → Yes, §§ 211, 212 StGB exist.

Lex certa – the statute must be sufficiently precise → “Mensch” is precise if you are Homo sapiens. It is not precise (in fact completely indeterminate) when the victim is an unknown extraterrestrial species.

Lex stricta – no punishment by analogy, no extension to the detriment of the defendant → This is the killer. → Extending the word “Mensch” in §§ 211/212 to include extraterrestrials would be a clear case of forbidden analogy that worsens the legal position of the accused. → German courts are constitutionally barred from doing this in criminal law (unlike in civil law or constitutional law, where they sometimes stretch concepts to protect victims).

Lex praevia – the law must have existed before the act → Also fulfilled, but irrelevant here.