There is no "truth" in court
There are only facts that are either contested or uncontested.
Uncontested facts are those agreed to by the parties, usually well before the hearing. They might be used in cross-examination to point out testimony that is inconsistent with what the parties have agreed and so cast doubt on the credibility of the witness.
Contested facts are, by definition, not agreed upon. Assuming the CCTV footage is admitted as evidence, it may be contested who the people in the images actually are or when the footage was actually shot or that the footage has been subsequently edited - such contested facts are perfectly legitimate matters to seek evidence on.
The lawyer doesn't know the facts - they only know what they have been told. It's likely that they have been told many conflicting things. Ask any group of 6 people what was decided in a meeting that concluded 20 minutes ago and you are likely to get 7 different answers. It's not that people are liars (although they sometimes are) is just that memory is not a hard drive, immutable and unchanging. Every time you access your memory you change it, overlaying the circumstances of each recollection onto it. Now imagine that there is some strong incentive on you for your memory of an event 18 months ago to be a certain way - say not going to jail or a lawsuit worth millions of dollars - this colors your memory. People remember things the way they wish they were rather than the way they actually were - this is not intentional (mostly).
The purpose of testimony is for these conflicting things to be tested - to be presented to the trier of fact so that they can decide which witnesses they believe and which they don't and draw their own conclusions as to what the facts (legally) are which may and often does differ materially from what each witness believes the facts are or even what the facts objectively are (presuming there is such a thing as an objective fact - law is not science; its a lot closer to history as an academic discipline).
Legal Limitations
In addition, there are strict limits on what is and is not allowed in cross-examination and the opposition council is very aware of what they are and will be very pro-active in requesting the judge enforce them by making an objection. A cross-examiner cannot lead ("At 8 pm that day, you were at the deli, correct?"), ask compound questions (“Did you determine the time of death by interviewing witnesses and by requesting the autopsy report written by the coroner?”), ask for a narrative, be argumentative (“Did you stop at the stop sign on 5th and Main?”, “No”, “So, to be clear, you ran the stop sign?”) or be vague (“When did you see it happen?”). However, if opposing counsel doesn't object the witness must answer.
Tactical Limitations
Nobody likes a bully. Overly aggressive cross-examination can be counterproductive and endear the witness to the fact-finder and make you look like a d^&k.
Ethics
A lawers ethical duty is not to the facts or, heaven forbid some notion of "truth", it is to present their evidence and to test their opponent's evidence so that their client's narrative (a non-fiction narrative) prevails.
In a civil case, that means showing that your version of the events is more likely than your opponents (balance of probabilities). In a criminal case, it means that the prosecutor must demonstrate beyond a reasonable doubt that all elements of the charge were perpetrated for a defendant - for a criminal defense lawyer, it means demonstrating that there is reasonable doubt in at least one of those elements.
It's also worth remembering that only contested matters go to trial - settlement, mediation, arbitration and plea bargains are far more common - and only the contested facts are the subject of cross-examination. Particularly in a civil trial, an agreed statement of facts is prepared to identify what's agreed and what's contested and evidence is only sought about the contested matters.
