“[前後]{ぜんご}” in this context means “approximately / around”.
It should be written as “30歳前後“ to make it clear that it refers to the age although we sometimes eliminate the part “歳(=age)” in informal conversations.
These two Kanjis have following meanings.
前=former, before, ... / 後= later, after, ...
Visually, it indicates something like this.
1, 2, 3, .... 30歳前(before thirties), 30, 30歳後(after thirtieth), ..., 41, 42, ....
“30歳前後と見られる男性” means “A man who is estimated to be around 30 years old”.
“~と見られる” can be translated as “estimated as~”.
It indicates probabilities, and is used when you don’t have a clear evidence for your guess.
For example,
サルと見られる動物 = An animal which is probably a monkey.
(You don’t have any evidence, but you are just guessing that it’s a monkey).
As for “ところで“, it implies his state/condition in this context.
“ところで” can be used to indicate states, conditions, circumstances, or situations in addition to its meaning as “place”.
For example,
- 犬が走っているところを見た。= I saw (the situation that) the dog was running.
- 彼が[苦]{くる}しんでるところを見た。= I saw the condition in which he was suffering.
The sentence as a whole is translated as...
Today, at around 11 am, at an apartment in Yokohama city, a man was found in the condition of being covered with blood and dead. Yokohama city police department has looked into the incident as a murder.
Hope it helps!